Metallkomplexe mit anionischen Liganden von Elementen der 4. Hauptgruppe. VIII. Pentacarbonyl-trihalogenstannido-metallat(O)-Komplexe von chrom,molybdän und wolfram mit fluor- und jodhaltigen stannidliganden

Metal Complexes with Anionic Ligands of Elements of the Main Group IV. VIII Pentacarbonyltrihalogenostannidometalate(O) Complexes of Chromium, Molybdenum, and Tungsten with Fluorine and Iodine Containing Trihalogenostannido Ligands In methylenechloride [As(C₆H₅)₄][SnF₃] readily reacts with the metalhexacarbonyls forming the arsoniumsalts of the pentacarbonyltrifluorostannidometalate(O) complexes, [M(CO)₅SnF₃]^? (M ? Cr, Mo, W). Exclusively by the reaction of the intermediately formed complex Cr(CO)₅THF only one pure triiodostannidometalate(O) Complex, [N(C₂H₅)₄][Cr(CO)₅SnJ₃], could be isolated. The trihalogenostannidometalate(O) complexes [M(CO)₅SnClX₂]^? (X ? F: M ? Cr, Mo, W; X ? J: M ? Cr) could be prepared by SnX₂-insertion reactions of the [M(CO)₅Cl]^? complexes. The bonding properties of the halogenostannide ions are discussed on the bases of the IR spectra of their metalate(O) complexes.     

Formation and dissociation mechanism of amide complexes III. Water substitution as the rate limiting factor for the interconversion of Cu2+ complexes with neutral and deprotonated amide groups

The protonation and deprotonation rates of the coordinated amide group in the Cu₂₊ complexes with N^α-(2-pyridyl-methyl)-glycinamide (I) and N^α-(2-pyridyl-methyl)-glycineethylamide (II) have been studied by stopped flow techniques. It is shown that the rate determining step of the formation of the complex with the deprotonated amide group is given by the rate of water dissociation from Cu₂₊. Weaker bases than OH^? or stronger acids than water can react by a different path, in which the proton transfer and/or the rotation from the O-co-ordinated into the N-co-ordinated form and vice versa is rate determining.     

Preparation of new monomers aza-β-aminoacids for solid-phase syntheses of aza-β-peptides

The preparation of new N^β-Fmoc-protected aza-β³-amino acids (aza-β³-aa) with proteinogenic side chains as well as their N^β-Fmoc, N^β-Cbz or N^β-Boc aza-β³-amino esters (from Pro, Asn, Asp, Glu, Gln) by successive nucleophilic substitutions will be described.     

Unusual heme-histidine bond in the active site of a chaperone

The heme chaperone CcmE is essential for the delivery of heme to c-type cytochromes. It forms an unusual transient, yet covalent, bond between an essential histidine, H130, and heme. We report on the discovery of the chemical structure of this bond solved by NMR, where the heme vinyl is cross-linked at the beta carbon to the Ndelta1 of H130. As this type of heme linkage has not been described previously in any cytochrome or hemoprotein, it represents a novel type of heme-histidine complex.     

The extraction of Cr(III) from aqueous thiocyanate solutions and its separation from Co(II) and Ni(II)

For the system liquid anion-exchanger—Cr(III)−NCS⁻, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing time of the Cr(III)−NCS⁻ solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10⁻⁴ M Cr(III) by 0.1M Aliquat in CCl₄ is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the complex anion present in the organic phase is Cr(NCS) ₆ ³⁻ ; when working with dilute metal ion solutions, the species extracted is Cr(NCS)₄ (H₂O) ₂ ⁻ . Separations of mixtures containing 10⁻²−10⁻⁴ M Co(II), Ni(II) and Cr(III) have successfully been accomplished.     

Enantioselective Diels-Alder reactions with N-hydroxy-N-phenylacrylamide

[reaction: see text] The use of hydroxamic acids as templates for Lewis acid catalyzed enantioselective Diels-Alder reactions has been examined. A very simple chiral Lewis acid, prepared by mixing optically pure binaphthol with 3 equiv of trimethylaluminum, catalyzes the [4 + 2] cycloaddition of N-hydroxy-N-phenylacrylamide with cyclopentadiene at 0 degrees C in high yield (>96%) and with a fairly good level of enantioselectivity (91% ee). Facile conversion of the products to the corresponding alcohols or aldehydes makes the hydroxamic acid intermediates particularly useful.     

Zur Kenntnis des Calciumbromats und - iodats,Kristallstruktur, röntgenographische,IR- und Raman-spektroskopische und thermoanalytische Untersuchungen

On Calcium Bromated and Iodates – Crystal Structure, X-Ray, IR and Raman Spectroscopical and Thermoanalytical Investigations The phase relationships (and both decomposition and disproportionation)of bromates and iodates of alkaline earth metals are studied by means of thermal analyses (DTA, DSC, TG) and (high-temperature) X-Ray, IR-, and (high-temperature) Raman spectroscopic measurements. The following compounds have been established: Ca(IO₃)₂ · 6 H₂O oF 216, the isotypic Ca(BrO₃)₂ · H₂O and Ca(IO₃)₂ · H₂O mP 48, Ca(IO₃)₂ I (Lautarit) mP 36, Ca(IO₃)₂ II and Ca(BrO₃)₂. The Crystal structure of Ca(IO₃)₂ · H₂O (brüggenite) (space group P2₁/c, Z = 4) has been determined by single crystal X-ray diffraction (MoKα). The final R value for 3888 reflections with I_o > 3σ₁ is 0.0487. The structures of bromates and iodates of alkaline earth metals known so far are discussed with respect to the energetic (mode frequencies) and geometric (bond lengths) distortion of the XO₃–ions as well as the strengths of H-bonds present in the respective hydrates.     

Synthesis of models of metabolites: Oxidation of variously substituted chromenes including acronycine,by a porphyrin catalytic system

The influence of chemical neighbouring on oxidation of substituted 2,2‐dimethylchromenes derivatives 5‐8 by a biomimetic catalytic system was first studied. It was then applied to acronycine an anti‐cancer drug in order to obtain in one single step oxidized products resulting from the reactivity of the 1,2‐double bond in the pyranic D‐ring. These 2,2‐dimethylchromenes constitute the structural moiety responsible for the activity of acronycine. This oxidation showed the sensitivity of the ethylenic bond, leading to the formation of the corresponding epoxides, diols and/or ketoalcohol. In the case of 5‐dimethylamino‐2,2‐dimethylchromene 8 , the double bond was not sensitive to oxidation, but the N‐methyl groups reacted to lead to the formamide derivative 16 and an imino‐alcohol 17 . This methodology applied to acronycine molecule 1 , allowed to obtain in one step, two oxidized compounds, a trans‐diol 3 and a ketoalcohol 4 under preparative conditions.     

Novel "Potentially antiaromatic", acidichromic quinonediimines with tunable delocalization of their 6 pi-electron subunits

We present a novel family of "potentially antiaromatic" alkyl-substituted p-benzoquinonediimine pH-dependent chromophores. It appears from the structural data that these overall 12 pi-electron molecules should be better considered as constituted by two chemically connected but electronically not conjugated 6 pi-electron subunits. Molecule 5 appears to be the first example of two separated, conjugated, and localized 6 pi-electron systems that can be tuned by reversible protonation to become delocalized. The mono- and diprotonated derivatives have been characterized by spectroscopic methods and X-ray diffraction. These systems develop supramolecular interactions in the solid state that clearly reflect the degree of protonation and depend on the nature of the counterion. These compounds constitute new chromophores for which the color can be tuned depending on the degree of protonation, going in solution from yellow for 5 to red for 5.HCl and blue for 5.2HCl. Theoretical calculations have provided a deeper insight into the electronic structure of these molecules and allowed an assignment of the experimental UV-vis spectra. The visible and near-UV spectrum of the neutral and protonated benzoquinonediimines can be classically assigned from the coupling of two 6 pi-electron polymethine units. TD-DFT calculations confirm the observed red shift of the two lowest pi --> pi* transitions of the benzoquinonediimines upon protonation and relate it to the moderate energy lowering of the HOMO --> LUMO transition induced by the delocalization of the polymethine pi system.     

Crystallization-induced asymmetric transformation of chiral-at-metal ruthenium(II) complexes bearing achiral ligands

Recently, we observed that the enantiopure Lambda form of the tributylammonium salt of the chiral anion tris[tetrachlorobenzene-1,2-bis(olato)]phosphate, also named Trisphat, was able to induce an efficient resolution of a Delta,Lambda racemic mixture of cis-[Ru(dmp)2(NCCH3)2](PF6)2 (dmp=2,9-dimethyl-1,10-phenanthroline) due to the spontaneous and selective precipitation of the heterochiral pair [Delta-Ru(dmp)2(CH3CN)2][Lambda-Trisphat]2. We report here that the combination of such a stereoselective precipitation process and irradiation results in the quantitative conversion of the initial [Ru(dmp)2(NCCH3)2]2+ racemate into only one of the two enantiomers. This is the first example in inorganic chemistry of an asymmetric transformation that leads to a chiral complex with no chiral ligand. Finally, three new racemic ruthenium bis(diimine) complexes, namely [Ru(dmp)2(NCCH3)Py](PF6)2 (Py=pyridine), [Ru(dmp)2(1,3-diaminopropane)](PF6)2, and [Ru(dmp)2(ethylenediamine)](PF6)2 were synthesized. For all of them, crystallization-induced asymmetric transformation proved to be an efficient way of obtaining the corresponding optically active chiral-at-metal complexes in high yields and with excellent stereoselectivities.